Technical Field
The present disclosure relates to a microelectromechanical device integrating a gyroscope and an accelerometer.
Description of the Related Art
As is known, the use of microelectromechanical systems (MEMS) has continued to spread to various sectors of technology and has yielded encouraging results especially in the production of inertial sensors, microintegrated gyroscopes, and electromechanical oscillators for a wide range of applications.
MEMS of this sort are usually based upon microelectromechanical structures comprising at least one mass connected to a supporting body (stator) through springs and movable with respect to the stator according to pre-set degrees of freedom. The movable mass and the stator are capacitively coupled through a plurality of respective comb-fingered and mutually facing electrodes, so as to form capacitors. The movement of the movable mass with respect to the stator, for example on account of an external stress, modifies the capacitance of the capacitors, whence it is possible to trace back to the relative displacement of the movable mass with respect to the fixed body and hence to the force applied. Conversely, by supplying appropriate biasing voltages, it is possible to apply an electrostatic force to the movable mass to set it in motion. Moreover, to obtain electromechanical oscillators, the frequency response of the inertial MEMS structures is exploited, which is typically of a second-order low-pass type, with a resonance frequency.
In particular, MEMS accelerometers exploit the fact that the displacements of the movable mass along the sensing axis or axes are correlated to the amplitude of the components of acceleration along the same axes to which the stator is subjected. These displacements are countered by the elastic action of the springs and can be sensed through the variations of the capacitive coupling, as mentioned above.
MEMS gyroscopes have a more complex electromechanical structure, which typically comprises two masses that are movable with respect to the stator and coupled together so as to have a relative degree of freedom. The two movable masses are both capacitively coupled to the stator. One of the masses is dedicated to driving and is kept in oscillation at the resonance frequency with controlled amplitude. The other mass is driven in oscillatory (translational or rotational) motion and, in the case of rotation of the microstructure with respect to a pre-set gyroscopic axis at an angular velocity, is subject to a Coriolis force proportional to the angular velocity itself. In practice, the driven mass, which is capacitively coupled to the fixed body through electrodes, like the driving mass, operates as an accelerometer that enables sensing of the Coriolis force and acceleration and hence makes it possible to trace back to the angular velocity. In some cases, a single mass is constrained to the stator so as to be movable with respect to the stator itself with two independent degrees of freedom. A driving device maintains the movable mass in controlled oscillation according to one of the degrees of freedom. The movable mass can then move according to the other degree of freedom in response to a rotation of the stator about a sensing axis, as a result of the Coriolis force.
In several applications, correct sensing of the translational and rotational movement of a device or of a part of a system is assuming increasing importance, and increasingly sophisticated solutions are required. For this reason, manufacturers have been pushed to equip the devices in question with sensors of various types, accelerometers and gyroscopes, so as to supply simultaneously measurements of acceleration and of angular velocity.
Currently, distinct devices are provided, possibly packaged in one and the same package. The solution presents, however, limitations, both in terms of overall dimensions, and in terms of levels of consumption, i.e., as regards aspects that are perceived as critical in modern microelectronics.